1. Field of the Invention
The present invention relates to means for carrying or conveying loads with the aid of a liquid cushion and more specifically is concerned with hydrostatic support structures and liquid-cushion load-carrying apparatus incorporating such support structures.
The proposed hydrostatic support structure may be used to convey heavy large-size loads for short distances on smooth horizontal or inclined bearing surface impermeable for the liquid used to form the liquid cushion.
This hydrostatic support structure may be employed, for example, to convey large products and structures of metal, concrete, etc. within shops and over the area of works. In some instances, apparatus with the proposed hydrostatic support structure can substitute for conventional load-handling equipment, such as cranes. The proposed hydrostatic support structure is most suitable to convey ship structures in erecting a ship hull on a slip-way and launch ships from inclined slipways.
2. Description of the Prior Art
The use of air-cushion load-carrying apparatus, such as the Rolair bearings produced by the U.S. company Rolair Systems Inc. (California), is well known in the art. The practice of operating such apparatus has shown them to be in many instances more economically efficient than conventional trailers or rail flatcars. Another significant advantage of the apparatus is that they allow the loads to be conveyed in any direction. Certain difficulties arise, however, as the weight of the load conveyed on an air-cushion apparatus increases. Employing apparatus with a low air pressure will entail a very high air consumption rate and hence a very high compressor power per ton of the load conveyed or, in other words, high power consumption for conveying every ton of load. On the other hand, increasing the air pressure deteriorates the stability of such apparatus and gives rise to problems in selecting materials for air cushion enclosures ("skirts") and ensuring the required load lift above the bearing surface.
To overcome the problems, the changeover from an air cushion to a liquid cushion, such as water one, has been started. A liquid cushion allows the specific pressure on a surface whereon a load is conveyed (the bearing surface) to be drastically increased, up to 20 kgf/cm.sup.2 and over, with the result that the load-carrying capacity of a liquid-cushion apparatus will greatly exceed that of an air-cushion one of the same dimensions.
The liquid-cushion load-carrying apparatus typically comprise several hydrostatic support structures, high-pressure pumps, hoses to feed the liquid, instrumentation, and control equipment. The hydrostatic support structures (Often referred to as water bearings) constitute the most essential component of the apparatus; it is these hydrostatic support structures which will be described hereinafter.
The hydrostatic support structure of a liquid-cushion load-carrying apparatus, known as the Water Skate bearing ("Hoverfoil News", 1975, No. 3, pp. 12-14), comprises a housing which is a small sectional-construction platform or pallet and an elastic skirt secured to the pallet along the lower perimeter thereof. Water is pumped through holes in the housing into the space defined by the skirt until the water pressure exceeds the pressure of the load onto the pallet; at this moment, the water starts uniformly leaking at a certain rate under the skirt along the entire perimeter, thereby creating a bearing water film. Then the load is conveyed in the desired direction by applying a small traction effort. Water is supplied to the above-described hydrostatic support structure via a conventional flexible hose from a pump which can be spaced at the required distance from the support structure. Inasmuch as the use of only one support structure cannot fully ensure the stability of the load being conveyed, the weight of the load is distributed among at least three such support structures.
The operation of the above-described hydrostatic support structure involves a high water consumption rate (60 l/min at a load-carrying capacity of 60 t), which substantially restricts its practical application.
A much lower liquid consumption rate is offered by another conventional hydrostatic support structure disclosed in British Pat. No. 1,377,807. The housing of the hydrostatic support structure has a recess communicating with a source of liquid for the formation of a liquid cushion and a groove disposed concentrically with said recess and accommodating a flexible sealing member. The groove has a nonuniform cross-section diverging towards the bearing surface. The sealing member accommodated in the groove is hollow, has as well a nonuniform (essentially a pear-shaped) cross-section, and is filled with liquid in operation. The rate of liquid consumption in operation of this hydrostatic support structure is cut down owing to that after the support structure is brought beneath the load, liquid under pressure is supplied into the groove and sealing member when the formation of the cushion has not yet been started; the action of the liquid causes the sealing member to bear tightly against the bearing surface and thereby to isolate the recess for the formation of the liquid cushion from the surroundings, i.e. to produce a closed contour of the cushion. While the cushion is being formed, the pressure in the sealing member is maintained such as to prevent the liquid from leaking thereunder until the load is lifted to the required (within the capacity of the support structure) height. When the load supported on the support structure is being moved, the ratio between the liquid pressures in the cushion and in the sealing member is maintained such that a thin film of the liquid exists under the seal. The thickness of the film, which is controllable, is maintained such as to allow the load to be moved under the traction effort with an insignificant consumption of the cushion liquid.
The above-described hydrostatic support structure makes it possible to considerably reduce the rate of cushion liquid consumption in operation. However, the manufacture and operation of the support structure involve certain difficulties which mainly stem from that the sealing member defining the liquid cushion along the perimeter thereof is acted upon, via the housing, by a considerable part of the weight of the load; this restricts the possibilities for increasing the load-carrying capacity of the support structure and calls for the use of a high-strength and dependable sealing member of an adequately flexible material, i.e. eventually of a rather complex and cumbersome sealing member. Moreover, for the liquid film thickness to be maintained within a predetermined range, the groove accommodating the sealing member must be permanently communicating with the source of liquid supplied under a high pressure.